The present invention relates to a process capable of producing, at a low cost in a high yield, high-purity pyridine derivatives serving as an important intermediate for the production of pharmaceuticals, agrichemicals, catalyst ligands, silver halide photosensitive materials, liquid crystals and electrophotography, and organic photosensitive materials or dyes used in the field of organic electroluminescence.
A variety of production processes of substituted pyridines have been reported. For example, reported is a process of condensing a pyridine compound and the N-oxide of another pyridine compound under heating in the presence of platinum-added Pd-C (Yakugaku Zasshi, 99(12), pp. 1176, 1181(1976)). The production yield is however low in this process. Also reported is cross-coupling reaction (Japanese Patent Laid-Open No. Sho 64-003169) making use of Grignard reaction, which is however accompanied with the such problems as difficulty in gaining or synthesizing a pyridine iodide compound necessary for obtaining a Grignard reagent of pyridines and necessity of special equipment.
In addition, proposed are Ullman condensation reaction of two pyridine halide compounds (Khim. Geol. Nauk., pp. 114(1970) and a process of cross-coupling a pyridine halide compound with a metal derivative in the presence of a Pd catalyst. For example, reported are cross-coupling with a borane derivative (Chem. Pharm. Bull., 33(11), pp. 4755(1985), Heterocycles, 23(9), pp. 2375(1985)), cross-coupling with an alkyl tin derivative (Tetrahedron Lett., 33, pp. 2199(1992)) and cross-coupling with a pyridine halide compound in the presence of an Ni catalyst (WO9852922).
For mass production, however, they involve many problems such as high cost of the catalyst or reagent employed for the reaction and necessity of special treatment for the metal waste. Moreover, existence of many byproducts of these reactions makes separation difficult and a product pure enough to use as an intermediate for pharmaceuticals or electron materials have not yet been obtained.
A process for synthesizing pyridine derivatives from a 1,2,4-triazine compound by using 2,5-norbornadiene is conventionally known (for example, Tetrahedron Lett., 39, pp. 8817, 8821, 8825 (1988)).
Upon use for mass production, however, 2,5-norbornadiene is accompanied with many problems that a large excess, more specifically, at least 10 equivalents is required relative to the amount of a substrate, reaction is not completed in a short time, it is expensive, it is so toxic that even slight suction of it causes headaches, and it has a problem in stable supply on an industrial scale.
A process for obtaining pyridine compounds by using 1,2,4-triazine and vinyl acetate is reported (Tetrahedron Lett., 59, pp. 5171(1969)), but its yield is low and in addition, a substrate usable for this process is limited to highly active 1,2,4-triazine having an alkoxycarbonyl group at the 3,5,6-positions.
An object of the present invention is to provide a process for producing high-purity pyridine derivatives useful as an intermediate of pharmaceuticals, agrichemicals or liquid crystals in a high yield and at a low cost, in which the process does not generate pollution problems and can be carried out on an industrial scale.
According to the present invention, the below-described processes for producing pyridine derivatives are provided and the above-described objet of the present invention is attained.
(1) A process for producing a pyridine derivative, which comprises reacting a 1,2,4-triazine compound with a vinyl carboxylate represented by the following formula (I): 
wherein R represents an alkyl group having at least 3 carbon atoms, a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic residue.
(2) The process for producing a pyridine derivative according to the item (1), wherein in the formula (I), R represents a alkyl group having 7 to 17 carbon atoms.
(3) The process for producing a pyridine derivative according to the item (1), wherein in the formula (I), R represents a substituted or unsubstituted phenyl group or a substituted or unsubstituted nitrogen-containing heterocyclic residue.
(4) The process for producing a pyridine derivative according to the item (1), which comprises reacting a 1,2,4-triazine compound represented by the following formula (III) with a vinyl carboxylate represented by the above-described formula (I): 
wherein R1, R2 and R3 may be the same or different and each represents a hydrogen atom, an alkyl group, an aryl group, a heterocyclic residue, an alkylthio group, an alkylsulfinyl group, an alkylsulfonyl group, an arylsulfinyl group, an arylsulfonyl group, an alkoxy group, a phenoxy group, an alkoxycarbonyl group or a phenoxycarbonyl group; R2 and R3 may be coupled together to form a ring.
(5) The process for producing a pyridine derivative according to the item (4), wherein in the formula (III), R1 represents a phenyl group or a nitrogen-containing heterocyclic residue.
(6) The process for producing a pyridine derivative according to the item (1), wherein the vinyl carboxylate is used in an amount of 1.01 to 20 moles per mole of the 1,2,4-triazine compound.
(7) The process for producing a pyridine derivative according to the item (1), wherein the vinyl carboxylate is used in. an amount of 1.5 to 5 moles per mole of the 1,2,4-triazine compound.
(8) The process for producing a pyridine derivative according to the item (1), wherein a reaction solvent having a boiling point of 100xc2x0 C. or greater is employed.
(9) The process for producing a pyridine derivative according to the item (1), wherein a reaction solvent having a boiling point of 180 to 250xc2x0 C. is employed.
(10) A process for producing a pyridine derivative, which comprises reacting a 1,2,4-triazine compound with a vinyl carboxylate derivative represented by the following formula (II): 
wherein n represents an integer of 0 to 18.
(11) The process for producing a pyridine derivative according to the item (10), wherein in the formula (II), n represents an integer of 3 to 12.
(12) The process for producing a pyridine derivative according to the item (10), which comprises reacting a 1,2,4-triazine compound represented by the following formula (III) with the vinyl carboxylate represented by the above-described formula (II): 
wherein R1, R2 and R3 may be the same or different and each represents a hydrogen atom, an alkyl group, an aryl group, a heterocyclic residue, an alkylthio group, an alkylsulfinyl group, an alkylsulfonyl group, an arylsulfinyl group, an arylsulfonyl group, an alkoxy group, a phenoxy group, an alkoxycarbonyl group or a phenoxycarbonyl group; R2 and R3 may be coupled together to form a ring.
(13) The process for producing a pyridine derivative according to the item (12), wherein in the formula (III), R1 is a phenyl group or a nitrogen-containing heterocyclic residue.
(14) The process for producing a pyridine derivative according to the item (10), wherein the vinyl carboxylate is used in an amount of 0.505 to 10 moles per mole of the 1,2,4-triazine compound.
(15) The process for producing a pyridine derivative according to the item (10), wherein the vinyl carboxylate is used in an amount of 0.75 to 2.5 moles per mole of the 1,2,4-triazine compound.
(16) The process for producing a pyridine derivative according to the item (10), wherein a reaction solvent having a boiling point of 100xc2x0 C. or greater is employed.
(17) The process for producing a pyridine derivative according to the item (10), wherein a reaction solvent having a boiling point of 180 to 250xc2x0 C. is employed.
The present invention will hereinafter be described more specifically.
In the vinyl carboxylate represented by the formula (I) or (II), R represents a linear, branched or cyclic alkyl group having at least 3 carbon atoms, a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic residue. As the substituent for the aryl or heterocyclic residue, those having a Hammett "sgr"m substituent constituent falling within a range of xe2x88x920.21 to 0.39 are usable. They may be monosubstituted or polysubstituted. When polysubstituted, substituents may be the same or different. Specific examples of the substituent having Hammett am falling within a range of xe2x88x920.21 to 0.39 include alkyl groups such as methyl and t-buytl, cycloalkyl groups such as cyclopentyl and cyclohexyl, aryl groups such as phenyl and naphthyl, alkoxy groups such as methoxy and ethoxy, amino groups such as amino and dimethylamino, a nitro group, and halogen atoms such as chlorine atom and bromine atom.
As R, examples of the linear, branched or cyclic alkyl groups having at least 3 carbon atoms, preferably at least 5 carbon atoms, more preferably 7 to 17 carbon atoms include propyl, isopropyl, butyl, isobutyl, s-butyl, t-buytl, butyl, pentyl, cyclopentyl, isopentyl, neopentyl, t-pentyl, 1-methylbutyl, 2-methylbutyl, 1-ethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, hexyl, cyclohexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1-ethylbutyl, 2-ethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,3-dimethylbutyl, 1,1-dimethylbutyl, 2,2-dimethylbutyl, 3,3-dimethylbutyl, 1-ethyl-2-methyl-propyl, heptyl, 1-methylhexyl, 2-methylhexyl, 3-methylhexyl, 4-methylhexyl, 5-methylhexyl, 1-ethylpentyl, 2-ethylpentyl, 3-ethylpentyl, 1,2-dimethylpentyl, 1,3-dimethylpentyl, 1,4-dimethylpentyl, 2,3-dimethylpentyl, 2,4-dimethylpentyl, 3,4-dimethylpentyl, 1,1-dimethylpentyl, 2,2-dimethylpentyl, 3,3-dimethylpentyl, 4,4-dimethylpentyl, 2-ethyl-1-methyl-butyl, 1-ethyl-2-methyl-butyl, 1-ethyl-3-methylbutyl, 1-ethyl-3-methylbutyl, 2-ethyl-3-methylbutyl, 1-ethyl-1-methylbutyl, 2-ethyl-2-methylbutyl, 1,2,3-trimethylbutyl, 1,1,2-trimethylbutyl, 1,2,2-trimethylbutyl, 1,1,3-trimethylbutyl, 1,3,3,-trimethylbutyl, 2,2,3-trimethylbutyl, 2,3,3-trimethylbutyl, 1-isopropyl-2-methylpropyl, octyl, 1-methylheptyl, 2-methylheptyl, 3-methylheptyl, 4-methylheptyl, 5-methylheptyl, 6-methylheptyl, 1-ethylhexyl, 2-ethylhexyl, 3-ethylexyl, 4-ethylhexyl, 1-propylpentyl, 2-propylpentyl, 1-butylbutyl, 1,2-dimethylhexyl, 1,3-dimethylhexyl, 1,4-dimethylhexyl, 1,5-dimethylhexyl, 2,3-dimethylhexyl, 2,4-dimethylhexyl, 2,5-dimethylhexyl, 3,4-dimethylhexyl, 3,5-dimethylhexyl, 4,5-dimethylhexyl, 1,1-dimethylhexyl, 2,2-dimethylhexyl, 3,3-dimethylhexyl, 4,4-dimethylhexyl, 5,5-dimethylhexyl, 1,2,3-trimethylpentyl, 1,2,4-trimethylpentyl, 2,3,4-trimethylpentyl, 2-ethyl-1-methylpentyl, 3-ethyl-1-methylpentyl, 1-ethyl-2-methylpentyl, 3-ethyl-2-methylpentyl, 1-ethyl-3-methylpentyl, 2-ethyl-3-methylpentyl, 1-ethyl-4-methylpentyl, 2-ethyl-1-methylpentyl, 1-ethyl-1-methylpentyl, 2-ethyl-2-methylpentyl, 3-ethyl-3-methylpentyl, 1,2-diethylbutyl, 1,1-diethylbutyl, 2,2-diethylbutyl, nonyl, isononyl, s-nonyl, t-nonyl, neononyl, decyl, isodecyl, s-decyl, t-decyl, neodecyl, undecyl, isoundecyl, s-undecyl, t-undecyl, neoundecyl, dodecane, isododecane, s-dodecane, t-dodecane, neododecane, tridecyl, isotridecyl, s-tridecyl, t-tridecyl, neotridecyl, tetradecyl, isotetradecyl, s-tetradecyl, t-tetradecyl, neotetradecyl, pentadecyl, isopentadecyl, s-pentadecyl, t-pentadecyl, neopentadecyl, hexadecyl, isohexadecyl, s-hexadecyl, t-hexadecyl, neohexadecyl, heptadecyl, isoheptadecyl, s-heptadecyl, t-heptadecyl, neoheptadecyl, octadecyl, isooctadecyl, s-octadecyl, t-octadecyl, neooctadecyl, nonadecyl, isononadecyl, s-nonadecyl, t-nonadecyl and neononadecyl.
Examples of the aryl group as R include phenyl, naphthyl, tolyl, xylyl, cumenyl, mesityl, dimethylaminophenyl, diphenylaminophenyl, methoxyphenyl, phenoxyphenyl, cyclohexylphenyl, nitrophenyl, chlorophenyl, bromophenyl, fluorophenyl, iodophenyl, trifluorophenyl, hydroxyphenyl, carboxyphenyl, methyloxycarbonylphenyl and cyanophenyl.
Examples of the heterocyclic residue as R include pyridyl, pyrazinyl, pyrimidyl, quinolyl, isoquinolyl, pyrrolyl, pyrazolyl, imidazolyl, thienyl, furyl, thiazolyl, isothiazolyl, oxazolyl, isoxazolyl, methylpyridyl, phenylpyridyl, nitropyridyl, chloropyridyl, bromopyridyl, methoxypyridyl, diphenylaminopyridyl, methylpyrazinyl, phenylpyrazinyl, nitropyrazinyl, chloropyrazinyl, bromopyrazinyl, methoxypyrazinyl and diphenylaminopyrazinyl.
In the formula (II), n stands for an integer of 0 to 18, preferably 3 to 12.
When, in the formula (I), R represents an alkyl group having 1 or 2 carbon atoms, the reaction between the 1,2,4-triazine compound and vinyl carboxylate proceeds very slowly. Such an alkyl group is therefore unsuited for the industrial production of pyridine derivatives.
In the formula (I), R preferably represents a C7-17 alkyl group. R representing a substituted or unsubstituted phenyl group or a substituted or unsubstituted nitrogen-containing heterocyclic residue is also preferred.
Specific preferred examples of R include propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl, pentyl, cyclopentyl, isopentyl, neopentyl, t-pentyl, 1-methylbutyl, 2-methylbutyl, 1-ethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, hexyl, cyclohexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1-ethylbutyl, 2-ethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,3-dimethylbutyl, 1,1-dimethylbutyl, 2,2-dimethylbutyl, 3,3-dimethylbutyl, heptyl, 1-methylhexyl, 2-methylhexyl, 3-methylhexyl, 4-methylhexyl, 5-methylhexyl, 1-ethylpentyl, 2-ethylpentyl, 3-ethylpentyl, 1,2-dimethylpentyl, 1,3-dimethylpentyl, 1,4-dimethylpentyl, 2,3-dimethylpentyl, 2,4-dimethylpentyl, 3,4-dimethylpentyl, 1,1-dimethylpentyl, 2,2-dimethylpentyl, 3,3-dimethylpentyl, 4,4-dimethylpentyl, octyl, 1-methylheptyl, 2-methylheptyl, 3-methylheptyl, 4-methylheptyl, 5-methylheptyl, 6-methylheptyl, 1-ethylhexyl, 2-ethylhexyl, 3-ethylexyl, 4-ethylhexyl, 1-propylpentyl, 2-propylpentyl, 1-butylbutyl, 1,2-dimethylhexyl, 1,3-dimethylhexyl, 1,4-dimethylhexyl, 1,5-dimethylhexyl, 2,3-dimethylhexyl, 2,4-dimethylhexyl, 2,5-dimethylhexyl, 3,4-dimethylhexyl, 3,5-dimethylhexyl, 4,5-dimethylhexyl, 1,1-dimethylhexyl, 2,2-dimethylhexyl, 3,3-dimethylhexyl, 4,4-dimethylhexyl, 5,5-dimethylhexyl, 1,2-diethylbutyl, 1,1-diethylbutyl, 2,2-diethylbutyl, nonyl, isononyl, s-nonyl, t-nonyl, neononyl, decyl, isodecyl, s-decyl, t-decyl, neodecyl, phenyl, naphthyl, tolyl, xylyl, cumenyl, mesityl, nitrophenyl, chlorophenyl, bromophenyl, fluorophenyl, iodophenyl, trifluorophenyl, cyanophenyl, pyridyl, pyrazinyl, pyrimidyl, quinolyl, isoquinolyl, pyrrolyl, pyrazolyl, imidazolyl, thienyl and furyl.
As the 1,2,4-triazine compound, 1,2,4-triazine compounds represented by the following formula (III) are preferred. 
wherein, R1, R2 and R3 may be the same or different and each represents a hydrogen atom, an alkyl group, an aryl group, a heterocyclic residue, an alkylthio group, an alkylsulfinyl group, an alkylsulfonyl group, an arylsulfinyl group, an arylsulfonyl group, an alkoxy group, a phenoxy group, an alkoxycarbonyl group or a phenoxycarbonyl group; R2 and R3 may be coupled together to form a ring.
One embodiment of reacting the 1,2,4-triazine compound with the vinyl carboxylate will next be described specifically for detailed description of the invention process. It should however be noted that the scope of the present invention is not limited to or by it.
The reaction between the 1,2,4-triazine compound (III) and the vinyl carboxylate proceeds in accordance with the below-described reaction scheme, whereby the corresponding pyridine derivative (a) is produced. 
wherein, R has the same meaning as described above, n stands for an integer of 0 to 18, preferably an integer of 3 to 12, and R1, R2 and R3 have the same meanings as described above.
A detailed description will next be made of R1, R2 and R3 in the formulas (a) and (III).
As examples of the alkys group, linear or branched C1-18 alkyl groups can be mentioned. Preferred examples include C1-4 alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl and tert-butyl. Of these, a methyl group which can be introduced into a carboxylic acid or aldehyde is more preferred.
As the aryl group, substituted or unsubstituted phenyl groups, naphthyl group, anthryl group and phenanthryl group can be given. Preferred examples include substituted or unsubstituted phenyl groups and naphthyl groups, with substituted or unsubstituted phenyl groups being more preferred.
As examples of the substituent for the substituted aryl group, substituents having a Hammett "sgr"m substituent constituent falling within a range of xe2x88x920.21 to 0.39 can be mentioned. They may be monosubstituted or polysubstituted. When polysubstituted, substituents may be the same or different. Specific examples of the substituent having Hammett "sgr"m falling within a range of xe2x88x920.21 to 0.39 include alkyl groups such as methyl and t-butyl, cycloalkyl groups such as cyclopentyl and cyclohexyl, aryl groups such as phenyl and naphthyl, alkoxy groups such as methoxy and ethoxy, amino groups such as amino and dimethylamino, nitro group, and halogen atoms such as chlorine atom and bromine atom.
Specific examples of the heterocyclic residue include substituted or unsubstituted pyridyl, pyrazinyl, pyrimidyl, quinolyl, isoquinolyl, pyrrolyl, pyrazolyl, imidazolyl, thienyl, furyl, thiazolyl, isothiazolyl, oxazolyl and isoxazolyl groups. Of these, preferred are substituted or unsubstituted pyridyl, pyrazinyl, pyrimidyl, quinolyl, isoquinolyl, pyrrolyl and pyrazolyl groups, with substituted or unsubstituted pyridyl, pyrazinyl, pyrimidyl, quinolyl and isoquinolyl groups being more preferred.
As examples of the substituent for the substituted heterocyclic residue, substituents having a Hammett "sgr"m substituent constituent falling within a range of xe2x88x920.21 to 0.39 can be mentioned. They may be monosubstituted or polysubstituted. When polysubstituted, substituents may be the same or different. Specific examples of the substituent having Hammett xcex4m falling within a range of xe2x88x920.21 to 0.39 include alkyl groups such as methyl and t-buytl, cycloalkyl groups such as cyclopentyl and cyclohexyl, aryl groups such as phenyl and naphthyl, alkoxy groups such as methoxy and ethoxy, amino groups such as amino and dimethylamino, nitro group, and halogen atoms such as chlorine atom and bromine atom.
Specific examples of the alkylthio group include linear or branched C1-18 alkylthio groups, preferably C1-4 alkylthio groups such as methylthio, ethylthio, propylthio, isopropylthio, butylthio, sec-butylthio and tert-butylthio, more preferably methylthio and ethylthio.
As examples of the alkylsulfinyl (xe2x80x94SOR) and alkylsulfonyl (xe2x80x94SO2R) groups, alkylsulfinyl and alkylsulfonyl groups having similar alkyl groups to those of the alkylthio group can be given. Preferred are methylsulfinyl, ethylsulfinyl, methylsulfonyl and ethylsulfonyl groups.
As examples of the arylsulfinyl (xe2x80x94SOAr) group, arylsulfinyl groups having a substituted or unsubstituted aryl group can be given and preferred are benzenesulfinyl and toluenesulfinyl groups.
As examples of the substituent for the substituted arylsulfinyl group, substituents having a Hammett "sgr"m substituent constituent falling within a range of xe2x88x920.21 to 0.39 can be mentioned. They may be monosubstituted or polysubstituted. When polysubstituted, substituents may be the same or different. Specific examples of the substituent having Hammett "sgr"m falling within a range of xe2x88x920.21 to 0.39 include alkyl groups such as methyl and t-butyl, cycloalkyl groups such as cyclopentyl and cyclohexyl, aryl groups such as phenyl and naphthyl, alkoxy groups such as methoxy and ethoxy, amino groups such as amino and dimethylamino, nitro group, and halogen atoms such as chlorine atom and bromine atom.
As examples of the arylsulfonyl (xe2x80x94SO2Ar) group, arylsulfonyl groups having a substituted or unsubstituted aryl group can be given and preferred are benzenesulfonyl and toluenesulfonyl groups.
As examples of the substituent for the substituted arylsulfonyl group, substituents having a Hammett "sgr"m substituent constituent falling within a range of xe2x88x920.21 to 0.39 can be mentioned. They may be monosubstituted or polysubstituted. When polysubstituted, substituents may be the same or different. Specific examples of the substituent having Hammett "sgr"m falling within a range of xe2x88x920.21 to 0.39 include alkyl groups such as methyl and t-buytl, cycloalkyl groups such as cyclopentyl and cyclohexyl, aryl groups such as phenyl and naphthyl, alkoxy groups such as methoxy and ethoxy, amino groups such as amino and dimethylamino, nitro group, and halogen atoms such as chlorine atom and bromine atom.
Specific examples of the alkoxy group include linear or branched C1-18 alkoxy groups. Preferred are C1-4 alkoxy groups such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy and tert-butoxy, with linear C1-4 alkoxy groups such as methoxy, ethoxy, propoxy and butoxy being more preferred.
As the alkoxycarbonyl (xe2x80x94COOR) group, the alkoxycarbonyl groups having the above-described alkoxy group can be mentioned. Preferred are methoxycarbonyl and ethoxycarbonyl groups.
In the formula (III), R1, R2 and R3 may be the same or different and preferred examples include a hydrogen atom, an alkyl group, an aryl group or a heterocyclic residue. As R1, alkyl, aryl and heterocyclic residue are more preferred, with phenyl and nitrogen-containing heterocyclic residue being especially preferred.
It is preferred that R2 and R3 represent the same group.
The 1,2,4-triazine compound which is a starting substance of the present invention can be prepared in any one of the following processes (1) to (4).
(1) A process for obtaining a 1,2,4-triazine compound by reacting a cyanoheterocyclic compound with a hydrazine and then reacting the amidrazone thus derived by the above reaction with a diketone (Tetrahedron Lett., 39, pp. 8817, 8821, 8825(1998)). A production process of a 1,2,4-triazine compound by adding water to this reaction system has already been found (Japanese Patent Application No. Hei 11-167308). One embodiment of it will be described next. 
(2) A process for producing a 1,2,4-triazine compound through a cyanoheterocyclic compound, carbamate and then, amidorazone (J. Korean Chem. Soc., 39(9), pp. 755(1995)). One embodiment of it will be described next. 
(3) A process for producing a 1,2,4-triazine compound by reacting an acid hydrazide and a diketone with ammonium acetate in an acetic acid solvent (Tetrahedron, 1, pp. 103(1957)). One embodiment of it will next be described. 
(4) A process for producing a 1,2,4-triazine compound by reacting an xcex1-haloketone with an acid hydrazide (Tetrahedron, 33, pp. 1043(1977)). One embodiment of it will next be described. 
The vinyl carboxylate of the formula (I) or (II) usable in the present invention can be prepared readily from a carboxylic acid, which contains an alkyl group having at least 3 carbon atoms, a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic residue, by the process as described below, but the production process is not limited thereto. Such vinyl carboxylates are easily available because various ones are put on the market. Commercially available ones may be used as they are.
Examples of the production process of the above-described vinyl carboxylate include the direct vinylation process (J. Am. Chem. Soc., 69, pp. 2439(1947), J. Polymer. Sci., 1, pp. 207 (1951), Trans. Faraday Soc., 49, pp. 1108(1953), U.S. Pat. No. 2,992,246 (1961), European Polymer J., 4, pp. 373(1968)), the vinyl exchange process (J. Org. Chem., 25, pp. 623(1960), Makromol. Chem., 73, pp. 173(1964)), Makromol. Chem., 29, pp. 119(1959), J. Polymer Sci., 27, pp. 269(1958), Kobunshi Kagaku, 17, pp. 227(1960), J. Sci. Eng. Res. Indian Inst. Technol. Kharagpur, 4, pp. 265(1990)), and the Halcon process (J. Am. Chem. Soc., 81, pp. 2552(1959)).
Specific examples of the vinyl carboxylate include vinyl butyrate, vinyl hexanoate, vinyl octanoate, vinyl decanoate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl pivalate, vinyl octylate, vinyl monochloroacetate, divinyl adipate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl benzoate, vinyl cinnamate, vinyl neodecanoate, vinyl neononanoate, vinyl 4-t-butylbenzoate, vinyl trifluoroacetate, vinyl-2-pyridine carboxylate, vinyl nicotinate, vinyl isonicotinate, vinyl-2-floate, vinyl 2-thiophenecarboxylate and divinyl adipate.
Of these, preferred are vinyl butyrate, vinyl hexanoate, vinyl octanoate, vinyl decanoate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl cyclohexanecarboxylate, vinyl pivalate, vinyl octylate, vinyl benzoate, vinyl neodecanoate, vinyl neononanoate, vinyl trifluoroacetate, and divinyl adipate, with vinyl hexanoate, vinyl octanoate, vinyl decanoate, vinyl laurate, vinyl cyclohexanecarboxylate, vinyl octylate, vinyl benzoate, vinyl neodecanoate, vinyl neononanoate, and divinyl adipate being especially preferred because of their easy separability after completion of the reaction.
There is no limitation imposed on the amount of the vinyl carboxylate insofar as it is at least an equimolar amount relative to the 1,2,4-triazine. The vinyl carboxylate of the formula (I) is usually used in an amount ranging from 1.01 to 20 moles, preferably 1.2 to 10.0 moles, more preferably 1.5 to 5.0 moles, each relative the 1,2,4-triazine (1 mole). The vinyl carboxylate of the formula (II), on the other hand, has two reaction sites in its molecule so that half the amount of the above case is sufficient for the progress of the reaction. Described specifically, the vinyl carboxylate of the formula (II) is usually employed in an amount ranging from 0.505 to 10 moles, preferably 0.6 to 5.0 moles, more preferably 0.75 to 2.5 moles, each relative to the 1,2,4-triazine (1 mole).
In the present invention, use of the reaction solvent is not indispensable, but preferred is a solvent having a boiling point of 100xc2x0 C. or greater, more preferably 130 to 300xc2x0 C., still more preferably 180 to 250xc2x0 C.
As the reaction solvent, aromatic compounds are preferred.
The followings are aromatic compounds having a boiling point of 100xc2x0 C. or greater and usable as the reaction solvent.
(i) Aromatic Hydrocarbon Compounds
Toluene, xylene, diethylbenzene, diisopropylbenzene, ethylbenzene, propylbenzene, butylbenzene, 1-phenylhexane, chlorobenzene, dichlorobenzene, trichlorobenzene, bromobenzene, dibromobenzene, methoxybenzene, methoxyphenol, dimethoxybenzene, nitrobenzene, 1,4-cyclohexylbenzene, diphenylmethane, 1,2,3,4-tetrahydronaphthalene and the like.
(ii) Aromatic Heterocyclic Compounds
2,4-Dichloropyrimidine, 2,3,5-trichloropyridine, quinoline, quinazoline, 1,4-benzodioxane and the like.
(iii) Hydrogenated Aromatic Heterocyclic Compounds
1,2,3,4-Tetrahydroquinoline, 5,6,7,8-tetrahydroquinoline, 1,2,3,4-tetrahydroisoquinoline, 5,6,7,8-tetrahydroisoquinoline, 1-phenylpiperidine, 1-phenylpiperazine, indoline, julolidine and the like.
The followings are aliphatic compounds having a boiling point of 100xc2x0 C. or greater and usable as a reaction solvent.
(iv) Saturated Aliphatic Compounds
Octane, nonane, decane, undecane, dodecane, tridecane, ethylcyclohexane, 2-methyldodecane, 4-ethylundecane, tetradecane, pentadecane, 3,3-dimethyltridecane, hexadecane, heptadecane, 2-methyl-4-ethyltetradecane, and the like.
(v) Saturated Cyclic Aliphatic Compounds
Dicyclohexyl, decahydronaphthalene, dodecahydrofluorene and the like.
(vi) Saturated Heterocyclic Aliphatic Compounds 1,3-Dimethyl-2-imidazolidinone (DMI), 1,4,7-trithiacyclononane, 1,4,7-trithiacyclodecane, 1,4,7,10-tetraoxacyclododecane, 1,4,7,10,13-pentaoxacyclopentadecane, 1,4,7-triazacyclononane and 1,4,7,10-tetraazacyclododecane.
These solvents may be used either singly or in combination as a reaction solvent.
Of the above-described reaction solvents, diethylbenzene, diisopropylbenzene, quinoline, nitrobenzene and 1,3-dimethyl-2-imidazolidinone (DMI) are preferred, with diisopropylbenzene and diethylbenzene being especially preferred. By the use of such a solvent, the reaction time can be shortened and the target compound can be obtained in a high yield.
The reaction solvent is usually employed in an amount ranging from 1 to 1000 ml, preferably 5 to 500 ml, more preferably 10 to 200 ml, relative to 0.1 mole of the 1,2,4-triazine.
The reaction temperature usually ranges from 80 to 350xc2x0 C., preferably 120 to 300xc2x0 C., more preferably 180 to 250xc2x0 C. The disappearance of the 1,2,4-triazine compound can usually be confirmed when reaction is conducted for 3 to 6 hours.
After completion of the reaction, dilute hydrochloric acid is added to transfer the target compound to the water layer, followed by separation into layers. After the water layer is made basic, it is extracted into a solvent such as ethyl acetate or toluene. The solvent is then concentrated under reduced pressure. An alcohol or hexane is added to the residue to crystallize the same, whereby a high-purity pyridine derivative is available. Purification may be conducted through distillation.
Specific preferred examples of the pyridine derivatives available by the present invention will next be shown as (A-1) to (D-11). It should however be borne in mind that the present invention is not limited to or by them. 